This application claims the benefit of Japanese Patent Application No. 2000-189861 which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an illumination apparatus for a microscope, and particularly to an illumination apparatus for microscope which is suitable for a photographing operation of a digital camera, or the like.
2. Related Background Art
Recently, a video image of high quality can be obtained with advancement in digital cameras with higher pixels. Though an image observed by a microscope was conventionally recorded by silver salt photography mainly, photography with a digital camera is increasingly employed for this purpose. Furthermore, in the fields of biology and medical treatments, electronization of clinical records is recently proposed. In addition, in the industrial fields, an image phototaken by a digital camera or a video camera is often observed by a television monitor, rather than by visual inspection, so as to improve a throughput in the inspecting process. Thus, it is estimated that further digitization advances in the field of observation by a microscope.
However, a charge coupled device (CCD) used in a digital camera, or the like, is sensitive to a change in brightness, compared with a film used for the silver salt photography. For this reason, in an image pickup operation by a digital camera, irregular illumination which was not a substantial problem in the prior art becomes a very serious drawback. As a result, there is a demand for an illumination system with less irregularity in illumination, compared with a conventional one, also in an illumination apparatus for a microscope.
The present invention was contrived taking the above problem into consideration, and an object of the invention is to provide a microscopic illumination apparatus which exhibits less irregularity in illumination and can obtain an excellent observed image even when using a digital camera, or the like.
In order to solve the above problem, according to the present invention, there is provided a microscopic illumination apparatus, comprising:
a light source for supplying illumination light;
a collector lens for converting a divergent light flux emitted from the light source into substantially parallel light fluxes;
a fly-eye lens disposed at a rear focal position of the collector lens; and
a relay optical system for relaying a pseudo plane light source which is formed on an exit end surface of the fly-eye lens to an aperture stop or a surface conjugate to the aperture stop,
wherein the following conditions are satisfied:
(1) 8xe2x89xa6fxe2x89xa624; and
(2) 1xe2x89xa6dxe2x89xa63,
where f is the focal length of one element for constituting the fly-eye lens, and d is the radius of the one element for constituting the fly-eye lens; and
the unit in the conditions (1) and (2) is preferably xe2x80x9cmmxe2x80x9d.
The conditions (1) and (2) define an appropriate focal length and radius of the element for constituting the fly-eye lens. Below the lower limit of both of the conditions (1) and (2), the size of the fly-eye lens is reduced beyond manufacturing practicality. In addition, the manufacturing cost is increased. On the contrary, above the upper limit of the conditions (1) and (2), the distance between the fly-eye lens and the relay lens following this fly-eye lens is increased, whereby the size of the illumination system is also increased. In addition, with the enlargement of each element of the fly-eye lens, the averaging effect of the illumination light is decreased.
According to a preferred embodiment of the invention, a cross section of the optical element for constituting the fly-eye lens is preferably hexagonal. In case the cross section is hexagonal, d denotes the radius of a circle inscribed in the hexagon.
According to another preferred embodiment, the relay optical system is preferably a reduction relay system. With this relay system, a bright image can be obtained.
According to still another preferred embodiment, the relay optical system preferably contains at least one or more cemented lenses. The reason that the relay optical system employs a cemented lens is to correct an aberration when a field stop FS is imaged on a sample surface.
According to still another preferred embodiment, it is preferable that a diffusing plate is inserted into a space between the fly-eye lens and the relay optical system, whereby pupil unevenness can be prevented.
According to still another preferred embodiment, the fly-eye lens is preferably manufactured by integral injection molding of plastic or glass. For instance, it is possible to manufacture, by integral injection molding, two optical members each having one surface on which each element of the fly-eye lens has a curvature and the other surface which is formed flat, so as to use these two members in such a manner that the flat surfaces of the both members are opposite to each other. Since an air layer is provided in this manner, the size of the apparatus can be compact when the focal length is the same. Also, compared with a case in which the whole fly-eye lens is integrally formed, the volume of a member to be pressed can be decreased, so as to reduce an amount of thermal contraction after pressing.